Underpinnings for securing electrical cables with plastic or rubber insulating sheaths to housings of spark-plug assemblies frequently include a rubber ring which is traversed by the cable and inserted in a cable inlet in the form of a pipe stub. A screw mounted in this pipe connector compresses the ring, whereby the same attains a friction lock with the cable and the pipe connector. Although the compressed rubber ring has proven to be effective in preventing relative rotation and axial motion of the cable and the pipe in many applications, increased load conditions have given rise to a need for a stronger and more secure underpinning assembly. Another disadvantage of the underpinnings using a rubber clamping and sealing ring is a high cost due to production and assembly of many components.